1. Field of the Invention
This invention relates generally to the art of extinguishing fires through the use of novel extinguishing agents.
More particularly, this invention relates to the use of combustible high molecular weight thermoplastic polymers as fire control and extinguishing agents.
In one specific embodiment, this invention relates to the use of fire extinguishing compositions containing high molecular weight polymers to suppress and extinguish burning flammable liquids.
2. Description of the Related Art
Combatting fires in flammable liquids (Class B fires) is generally recognized as presenting one of the most difficult challenges in the art of fire fighting. It is conventional to use either dry chemicals or foams in combating such fires. Each of those types of fire extinguishing agents has its own advantages and deficiencies.
Dry chemicals useful in fire fighting include a variety of alkali and alkaline earth metal compounds and other salts, probably the most well known being sodium bicarbonate. The use of sodium bicarbonate as an extinguishing agent goes back at least a century and it is still in common use today. Potassium bicarbonate formulations came into use about 1959 and these agents, which came to be know as "Purple K", have about twice the flame quenching capacity per unit weight as do the analogous sodium bicarbonate formulations. Later, another dry chemical formulation based on potassium chloride was developed and this formulation is known as "Super-K".
Another group of compounds which have found extensive recent use in dry chemical formulations are the ammonium phosphates, particularly monoammonium phosphate (ammonium dihydrogen phosphate). That compound has about the same extinguishing effectiveness toward flammable liquids as does sodium bicarbonate. It breaks down in the heat of the flame to leave a glassy residue or coating comprising metaphosphoric acid. Ammonium polyphosphates have also found use in dry chemical formulations. These compounds are prepared by heating polyphosphoric acid and reacting the heated mixture with ammonia as is described in U.S. Pat. No. 3,755,163. That patent asserts that the polyphosphates are more effective fire extinguishing agents on a weight basis than are the primary or secondary ammonium phosphates.
Probably the most effective dry chemical fire extinguishing agents are those formulations based on a carbamic powder which is an addition product of urea with potassium bicarbonate. Such products are sold under the tradename "Monnex" and are reportedly some twice or more as efficient as potassium bicarbonate for flame extinction. An example of a Monnex formulation is found in U.S. Pat. No. 3,947,365.
All of those dry chemical fire extinguishing agents achieve rapid extinguishment of flames in burning hydrocarbons and other flammable substances but all have a common fault. None have a lasting, or securing effect on the fuel source and so a fire tends to repeatedly reignite or flash back so long as there is an ignition source in contact with flammable vapors. It is postulated in the art that reignition occurs because the powder extinguishment agent is wetted as it contacts the surface of the burning liquid and, because it is more dense than is the liquid, sinks in the liquid. Once the agent is immersed in the liquid, its usefulness as an extinguishing or flame-inhibiting agent is lost.
A flammable liquid can be secured against reignition by use of a foam agent which floats on the surface of the liquid and acts to extinguish flames by isolating fuel vapors from the atmosphere. Such foam agents may comprise, for example, an aqueous blend of a flurorosurfactant and a hydrolysed protein or may be a film-forming foam based on fluorosurfactants known commercially as "AFFF" compositions. Examples of such compositions are shown in U.S. Pat. No. 4,424,133. Foam must be applied to the surface of the burning liquid and allowed to flow over the entire burning area. Foam-type extinguishing agents are generally much slower in operation than are dry chemical agents. Further, the use of foams can be greatly disrupted by air flow or by wind which tends to strip the foam from the liquid surface.
A number of attempts have been made to overcome the deficiencies of both the traditional dry chemical and foam fire extinguishing agents. An anti-reflash dry chemical agent is described in U.S. Pat. No. 3,553,127 to Warnock et al. That patent describes a dry powder fire extinguishing composition comprising a conventional powder base material, such as an alkali metal bicarbonate, which has a fluorocarbon surfactant adsorbed on its surface. The powder particles having a surfactant coating are resistant to wetting by liquid fuels and cause the particles to float on the liquid surface. Those floating particles produce a film or barrier on the liquid surface which tends to retard evaporation of the liquid and inhibits reignition of the unburned fuel portion.
Certain polymeric materials have also been proposed for use in fire extinguishing compositions. The Siimes patent, U.S. Pat. No. 3,179,588, for example, discloses use of a phenolic resin and a silicone resin in combination with an ammonium phosphate, an alkali metal sulfate, mica and magnesium or zinc stearate. The phenolic resin is said to modify the particle form of the powdered phosphate and sulfate metal salts. Phenolic resins satisfactory for use may suitably be a phenol-aldehyde condensation product so long as it is a B-stage reaction product and is in powder form. A B-stage phenolic resin is one that is partially reacted to a stage where it is insoluble in hydrocarbons and common organic solvents but remains plastic during a limited period of heat working. Ordinarily, a B-stage resin is heated and shaped by the user during which the resin is converted to the C-stage. A C-stage phenolic resin is insoluble in essentially all solvents and cannot be melted or softened by reheating. The silicone resin used by Siimes functions to form an external shell on the powder particles to impart water repellency to the particles.
U.S. Pat. No. 4,402,363 to Klein uses polymer "micro-bits" in a water slurry to put out fires. A polymer micro-bit is a foamed plastic such as foamed polystyrene or foamed polyurethane which has been shredded or pulverized to form small particles. Each of those particles absorbs and holds water. According to the patent, the micro-bits adhere or stick to a burning surface. That allows all of the water contained in each micro-bit to be fully utilized in producing steam which both cools the fire surface and tends to exclude oxygen from the flame.
Yet another approach is illustrated by the patent to Hisamoto et al, U.S. Pat. No. 4,606,832. That patent describes a fire extinguishing composition comprising a mixture of Halon (which is the trademark for bromofluorohydrocarbon or bromochlorohydrocarbon extinguishing agents) with a fluorine-containing polymer having a molecular weight in excess of 5,000 and preferably having a molecular weight in excess of 10,000. The composition is stated to be particularly useful in combatting oil or grease fires as the fluorine-containing polymer forms a heat resisting film on the oil surface thereby tending to prevent reignition of the unburned fuel.
In all of those prior art approaches to the extinguishing of burning flammable liquids, the unburned portion of the flammable liquid remains mobile and will reignite if the foam or film covering the surface of the liquid is disrupted. Further, the unburned mobile liquid is free to drain or travel to a new location thus spreading the fire as often occurs with fuel fires aboard ships.
Thus it can be readily appreciated that a fire extinguishing composition which rapidly suppresses the flame of a burning flammable liquid and also substantially decreases the mobility and flammability of the unburned liquid provides important advances in the art of fire fighting.